The present invention relates to a night vision system for detecting objects at relatively low visible light levels. In particular, the invention concerns an active night vision system having an anti-blinding scheme employing pulsed illumination and synchronization with detected pulsed light sources from approaching vehicles.
Night vision systems are utilized to allow a user to see objects at relatively low visibility light levels. Night vision systems are typically classified as either passive night vision systems or active night vision systems. In known passive night vision systems used in automotive applications, mid-infrared cameras are used to image objects using the ambient infrared light emitted by the objects in the environment.
Known active night vision systems utilize a near-infrared (NIR) laser diode or a filtered incandescent light source to generate NIR light. The NIR light is subsequently reflected off objects in the environment and is received by a NIR-sensitive camera. The camera generates a video signal responsive to received light.
A problem encountered by night vision systems is blinding, wherein two vehicle including night vision systems approach each other.
One solution to night vision system blinding by oncoming vehicles similarly equipped with a NIR light source is provided in U.S. patent application Ser. No. 09/683,840 entitled “GPS-Based Anti-Blinding System For Active Night Vision.” In that application, GPS is used to determine the direction of travel of the vehicles as well as an absolute time reference. Vehicles proximate one another synchronize their pulsed light sources to the absolute time reference signal with the phase of the light pulse based on the direction of motion of the respective vehicles. In this way, two cars approaching one another from opposite directions will have their NIR light sources pulsed out-of-phase with each other at duty cycles below 50% to avoid having their light source “on” when the opposing vehicle's camera is also “on.” The disclosed anti-blinding scheme, however, requires that all night vision equipped vehicles must also be equipped with GPS systems.
Thus, there exists a need for alternate night vision systems and methods related thereto that mitigate or eliminate blinding of the vehicle's night vision system by similarly equipped approaching vehicles.